Electro-mechanical solenoids are used in many applications. A solenoid is an inductor, usually composed of a cylindrical or toroidal core surrounded by a coil. The core is axially displaced in response to a magnetic field generated by current flowing through the coil. The core is drawn into a position where the magnetism can flow completely through the core, as opposed to air. Solenoids are commonly used to cause linear actuation of an attached device. Solenoids are widely used for spark-ignition and compression-ignition engine starting motors, which may be used, for example, in motor vehicle, material handling, marine, generator, and lawn/garden applications.
Solenoids, by virtue of their structure and operation, are susceptible to malfunction due to entry of foreign contaminants. In addition, internal contaminants, such as water vapor and other atmospheric gases, can adversely affect solenoid operation if allowed to accumulate. For example, water condensation on internal solenoid surfaces can result in oxidation of internal solenoid components. Condensation can also cause ice formation on internal components. Solenoid designs must therefore provide adequate protection from external contaminants while minimizing the amount of internal contaminant accumulation.
To cope with the adverse effects of contaminants, conventional solenoids often include air gaps around interface components. Additionally, conventional solenoids sometimes include small-diameter drain tubes and metal screen vents insert molded into the external walls of solenoid components. The injection molding is used to prevent liquid entry around the vents and also to prevent the vents from dislodging.
Conventional solenoid designs may be deficient in several aspects. Typical solenoid designs do not provide an effective and flexible means for allowing internal vapor to escape. Drain tubes, for example, leave the solenoid vulnerable to external contaminant entry. Drain tubes are also limiting in that they are often effective only when located at the bottom of a solenoid. Further, conventional designs do not provide effective control of the vapor transfer rate and the resistance to external contaminant entry. Additionally, insertion molding can be cost prohibitive and is suitable for only limited vent materials.